1. Field of the Invention
The present invention relates to a spindle motor that allows more excellent abrasion resistance and productivity exhibited by making each of kinetic pressure-generating grooves that generate fluid kinetic pressure in axial direction to be formed at position that is less influenced than ever by fluid material as thrust is integrally formed at driving shaft.
2. Description of the Prior Art
Generally spindle motor used in hard disk driver requires very high-speed driving force so that the motor employs fluid kinetic pressure bearing which has low drive load than at usual driving.
FIG. 1 shows an example of spindle motor applying conventional fluid kinetic pressure bearing, where are in large classification the fixed members of base plate 1, sleeve 2 and stator core assembly 3 and the rotating members of shaft 4, hub 5 and magnet 6 for comprising means of motor.
Sleeve 2 center has been holed through vertically so as to form an inner diameter part whose inner diameter has been enlarged at bottom part, to which inner diameter part a shaft 4 has been inserted to be able to revolve, which shaft has been bound by an interference fit with disk-shaped thrust 7 so that both of these can revolve together (at the inner diameter part side shaft 4 bottom part where the inner diameter has come widened as above).
And the bottom part of inner diameter part thus penetrated downward is isolated from outside by being covered by cover plate 8; and a cap-shaped hub 5 that is open downward is integrally combined at top part of shaft 4 inserted in sleeve 2.
In structure described above, usually a fine gap G is formed between inner diameter surface of sleeve 2 and thrust 7 and shaft 4 (inserted in the inner diameter part of sleeve 2 so that oil may float in gap G.
And kinetic pressure-generating grooves 2a are formed in shape as in FIG. 2 on upper and lower parts of inner diameter surface of sleeve 2 facing the outer cylindrical surface of shaft 4 intercalating the gap G in between; and kinetic pressure-generating grooves 7a are also formed as in FIG. 3 on top surface and bottom surface of thrust 7 that is bound at lower end portion of shaft 4.
Therefore oil floats through gap G between opposing surfaces of sleeve 2 and shaft 4 if motor is driven to rotate shaft 4 under condition where oil is filled in gap G (between the opposing surfaces of sleeve 2 and shaft 4.
Oil that floats thus is concentrated at kinetic pressure-generating grooves 2a that are formed respectively on upper and lower parts of inner diameter surface of sleeve 2 so that kinetic pressure is developed in radial direction of shaft; by which kinetic pressure generated thus, gap G (between the opposing surfaces of sleeve 2 and shaft 4 is always maintained uniformly.
And as thrust 7 bound at shaft 4 is accommodated at widened inner diameter part of sleeve 2, a certain is gap is also formed between stepwise-jawed inner cylindrical surface of sleeve 2 opposing top surface and bottom surface of thrust 7 and cover plate 8 top surface, through which gap the oil floats when motor is operated, which floating oil is concentrated at kinetic pressure-generating grooves 7a formed on top surface and bottom surface of thrust 7 so that kinetic pressure is developed in axial direction; by which kinetic pressure generated thus, gap between thrust 7 and its opposing surface is always maintained uniformly.
But there are some problems in part that generates fluid kinetic pressure in such conventional spindle motor.
Firstly, intense precision is required in processing inner diameter of thrust 7 as thrust 7 is assembled to shaft 4 by hot rolling, while inner diameter rectangularity control is very difficult where thrust 7 must be perpendicular to shaft 4.
And as kinetic pressure-generating grooves 7a formed on both sides of thrust 7 should be sequentially machined because simultaneous machining of the grooves is practically impossible, there arises machining deviation in the kinetic pressure-generating grooves 7a formed by such machining process.
Thrust 7 requires very difficult workmanship not only in processing of itself as above but also in assembling with shaft 4 so that productivity decrease is induced.
Secondly, as kinetic pressure-generating grooves 7a are formed at thrust 7 rotating simultaneously with shaft 4, thrust 7 abrasion resistance is deteriorated by severe friction with oil during shaft 4 rotation.
Thirdly, degrees of processing of kinetic pressure-generating grooves 7a formed on both sides of thrust 7 are made in noncongruity with each other because these both sides of grooves cannot be simultaneously machined; and particularly, because conventional shaft 4 and thrust 7 are made of SUS series metal while sleeve 2 is made to be furnished with stuff of brass or bronze that has higher thermal expansion coefficient than the above metal, gap G between shaft 4 and sleeve 2 and thrust 7 may be excessively wide open at high temperature because of thermal expansion coefficient diferrence of the above two kinds of materials, or deviation in gap G may be severely wide open so that there arise problems that severe vibration and noise are generated during motor operation and wear is accelerated.
Such problems result in a deterioration of drive performance of motor and a use life reduction so as to be product reliability deterioration factor.